[fpc-pascal] Visitor pattern (was: Weird interface behavior)

[Marco van de Voort]

In our previous episode, michael.vancanneyt at wisa.be said:
> >> class.
> >
> > Is this visitor pattern something that I should care about?
> > I have programmed quite much and never needed it.

> 
> You don't need to care about it. It's a pattern like any other.

(and the GoF, the authors of the book that initiated the pattern movement
warn against over use.  They wanted to provide a common jargon and write
down common experiences for others to mine for ideas, not to tell you what
to do.  Read their introduction, it is interesting)